From ac8843553af34855d0331554c03280e66c4ea582 Mon Sep 17 00:00:00 2001
From: Angel Pons <th3fanbus@gmail.com>
Date: Sun, 8 May 2022 00:05:41 +0200
Subject: [PATCH 21/26] haswell NRI: Add RcvEn training

Implement the RcvEn (Receive Enable) calibration procedure.

Change-Id: Ifbfa520f3e0486c56d0988ce67af2ddb9cf29888
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
---
 .../intel/haswell/native_raminit/Makefile.inc |   1 +
 .../haswell/native_raminit/raminit_main.c     |   1 +
 .../haswell/native_raminit/raminit_native.h   |  14 +
 .../haswell/native_raminit/reg_structs.h      |  13 +
 .../native_raminit/train_receive_enable.c     | 561 ++++++++++++++++++
 .../intel/haswell/registers/mchbar.h          |   3 +
 6 files changed, 593 insertions(+)
 create mode 100644 src/northbridge/intel/haswell/native_raminit/train_receive_enable.c

diff --git a/src/northbridge/intel/haswell/native_raminit/Makefile.inc b/src/northbridge/intel/haswell/native_raminit/Makefile.inc
index ebe9e9b762..e2fbfb4211 100644
--- a/src/northbridge/intel/haswell/native_raminit/Makefile.inc
+++ b/src/northbridge/intel/haswell/native_raminit/Makefile.inc
@@ -16,3 +16,4 @@ romstage-y += setup_wdb.c
 romstage-y += spd_bitmunching.c
 romstage-y += testing_io.c
 romstage-y += timings_refresh.c
+romstage-y += train_receive_enable.c
diff --git a/src/northbridge/intel/haswell/native_raminit/raminit_main.c b/src/northbridge/intel/haswell/native_raminit/raminit_main.c
index 5e4674957d..7d444659c3 100644
--- a/src/northbridge/intel/haswell/native_raminit/raminit_main.c
+++ b/src/northbridge/intel/haswell/native_raminit/raminit_main.c
@@ -60,6 +60,7 @@ static const struct task_entry cold_boot[] = {
 	{ configure_memory_map,                                   true, "MEMMAP",     },
 	{ do_jedec_init,                                          true, "JEDECINIT",  },
 	{ pre_training,                                           true, "PRETRAIN",   },
+	{ train_receive_enable,                                   true, "RCVET",      },
 };
 
 /* Return a generic stepping value to make stepping checks simpler */
diff --git a/src/northbridge/intel/haswell/native_raminit/raminit_native.h b/src/northbridge/intel/haswell/native_raminit/raminit_native.h
index 7c1a786780..a36ebfacd1 100644
--- a/src/northbridge/intel/haswell/native_raminit/raminit_native.h
+++ b/src/northbridge/intel/haswell/native_raminit/raminit_native.h
@@ -42,6 +42,9 @@
 #define NUM_WDB_CL_MUX_SEEDS	3
 #define NUM_CADB_MUX_SEEDS	3
 
+/* Specified in PI ticks. 64 PI ticks == 1 qclk */
+#define tDQSCK_DRIFT		64
+
 /* ZQ calibration types */
 enum {
 	ZQ_INIT,	/* DDR3: ZQCL with tZQinit, LPDDR3: ZQ Init  with tZQinit  */
@@ -188,6 +191,7 @@ enum raminit_status {
 	RAMINIT_STATUS_MPLL_INIT_FAILURE,
 	RAMINIT_STATUS_POLL_TIMEOUT,
 	RAMINIT_STATUS_REUT_ERROR,
+	RAMINIT_STATUS_RCVEN_FAILURE,
 	RAMINIT_STATUS_UNSPECIFIED_ERROR, /** TODO: Deprecated in favor of specific values **/
 };
 
@@ -270,6 +274,10 @@ struct sysinfo {
 
 	union ddr_data_vref_adjust_reg dimm_vref;
 
+	uint8_t io_latency[NUM_CHANNELS][NUM_SLOTRANKS];
+	uint8_t rt_latency[NUM_CHANNELS][NUM_SLOTRANKS];
+	uint32_t rt_io_comp[NUM_CHANNELS];
+
 	uint32_t data_offset_train[NUM_CHANNELS][NUM_LANES];
 	uint32_t data_offset_comp[NUM_CHANNELS][NUM_LANES];
 
@@ -344,6 +352,11 @@ static inline void clear_data_offset_train_all(struct sysinfo *ctrl)
 	memset(ctrl->data_offset_train, 0, sizeof(ctrl->data_offset_train));
 }
 
+static inline uint32_t get_data_train_feedback(const uint8_t channel, const uint8_t byte)
+{
+	return mchbar_read32(DDR_DATA_TRAIN_FEEDBACK(channel, byte));
+}
+
 /* Number of ticks to wait in units of 69.841279 ns (citation needed) */
 static inline void tick_delay(const uint32_t delay)
 {
@@ -401,6 +414,7 @@ enum raminit_status convert_timings(struct sysinfo *ctrl);
 enum raminit_status configure_mc(struct sysinfo *ctrl);
 enum raminit_status configure_memory_map(struct sysinfo *ctrl);
 enum raminit_status do_jedec_init(struct sysinfo *ctrl);
+enum raminit_status train_receive_enable(struct sysinfo *ctrl);
 
 void configure_timings(struct sysinfo *ctrl);
 void configure_refresh(struct sysinfo *ctrl);
diff --git a/src/northbridge/intel/haswell/native_raminit/reg_structs.h b/src/northbridge/intel/haswell/native_raminit/reg_structs.h
index b943259b91..b099f4bb82 100644
--- a/src/northbridge/intel/haswell/native_raminit/reg_structs.h
+++ b/src/northbridge/intel/haswell/native_raminit/reg_structs.h
@@ -297,6 +297,19 @@ union ddr_scram_misc_control_reg {
 	uint32_t raw;
 };
 
+union sc_io_latency_reg {
+	struct __packed {
+		uint32_t iolat_rank0     : 4; // Bits  3:0
+		uint32_t iolat_rank1     : 4; // Bits  7:4
+		uint32_t iolat_rank2     : 4; // Bits 11:8
+		uint32_t iolat_rank3     : 4; // Bits 15:12
+		uint32_t rt_iocomp       : 6; // Bits 21:16
+		uint32_t                 : 9; // Bits 30:22
+		uint32_t dis_rt_clk_gate : 1; // Bits 31:31
+	};
+	uint32_t raw;
+};
+
 union mcscheds_cbit_reg {
 	struct __packed {
 		uint32_t dis_opp_cas    : 1; // Bits  0:0
diff --git a/src/northbridge/intel/haswell/native_raminit/train_receive_enable.c b/src/northbridge/intel/haswell/native_raminit/train_receive_enable.c
new file mode 100644
index 0000000000..576c6bc21e
--- /dev/null
+++ b/src/northbridge/intel/haswell/native_raminit/train_receive_enable.c
@@ -0,0 +1,561 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <console/console.h>
+#include <northbridge/intel/haswell/haswell.h>
+#include <types.h>
+
+#include "raminit_native.h"
+#include "ranges.h"
+
+#define RCVEN_PLOT	RAM_DEBUG
+
+static enum raminit_status change_rcven_timing(struct sysinfo *ctrl, const uint8_t channel)
+{
+	int16_t max_rcven = -4096;
+	int16_t min_rcven = 4096;
+	int16_t max_rcven_rank[NUM_SLOTRANKS];
+	int16_t min_rcven_rank[NUM_SLOTRANKS];
+	for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+		max_rcven_rank[rank] = max_rcven;
+		min_rcven_rank[rank] = min_rcven;
+	}
+	for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+		if (!rank_in_ch(ctrl, rank, channel))
+			continue;
+
+		for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+			int16_t new_rcven = ctrl->rcven[channel][rank][byte];
+			new_rcven -= ctrl->io_latency[channel][rank] * 64;
+			if (max_rcven_rank[rank] < new_rcven)
+				max_rcven_rank[rank] = new_rcven;
+
+			if (min_rcven_rank[rank] > new_rcven)
+				min_rcven_rank[rank] = new_rcven;
+		}
+		if (max_rcven < max_rcven_rank[rank])
+			max_rcven = max_rcven_rank[rank];
+
+		if (min_rcven > min_rcven_rank[rank])
+			min_rcven = min_rcven_rank[rank];
+	}
+
+	/*
+	 * Determine how far we are from the ideal center point for RcvEn timing.
+	 * (PiIdeal - AveRcvEn) / 64 is the ideal number of cycles we should have
+	 * for IO latency. command training will reduce this by 64, so plan for
+	 * that now in the ideal value. Round to closest integer.
+	 */
+	const int16_t rre_pi_ideal = 256 + 64;
+	const int16_t pi_reserve = 64;
+	const int16_t rcven_center = (max_rcven + min_rcven) / 2;
+	const int8_t iolat_target = DIV_ROUND_CLOSEST(rre_pi_ideal - rcven_center, 64);
+
+	int8_t io_g_offset = 0;
+	int8_t io_lat[NUM_SLOTRANKS] = { 0 };
+	for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+		if (!rank_in_ch(ctrl, rank, channel))
+			continue;
+
+		io_lat[rank] = iolat_target;
+
+		/* Check for RcvEn underflow/overflow */
+		const int16_t rcven_lower = 64 * io_lat[rank] + min_rcven_rank[rank];
+		if (rcven_lower < pi_reserve)
+			io_lat[rank] += DIV_ROUND_UP(pi_reserve - rcven_lower, 64);
+
+		const int16_t rcven_upper = 64 * io_lat[rank] + max_rcven_rank[rank];
+		if (rcven_upper > 511 - pi_reserve)
+			io_lat[rank] -= DIV_ROUND_UP(rcven_upper - (511 - pi_reserve), 64);
+
+		/* Check for IO latency over/underflow */
+		if (io_lat[rank] - io_g_offset > 14)
+			io_g_offset = io_lat[rank] - 14;
+
+		if (io_lat[rank] - io_g_offset < 1)
+			io_g_offset = io_lat[rank] - 1;
+
+		const int8_t cycle_offset = io_lat[rank] - ctrl->io_latency[channel][rank];
+		for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+			ctrl->rcven[channel][rank][byte] += 64 * cycle_offset;
+			update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+		}
+	}
+
+	/* Calculate new IO comp latency */
+	union sc_io_latency_reg sc_io_lat = {
+		.raw = mchbar_read32(SC_IO_LATENCY_ch(channel)),
+	};
+
+	/* Check if we are underflowing or overflowing this field */
+	if (io_g_offset < 0 && sc_io_lat.rt_iocomp < -io_g_offset) {
+		printk(BIOS_ERR, "%s: IO COMP underflow\n", __func__);
+		printk(BIOS_ERR, "io_g_offset: %d\n", io_g_offset);
+		printk(BIOS_ERR, "rt_iocomp: %u\n", sc_io_lat.rt_iocomp);
+		return RAMINIT_STATUS_RCVEN_FAILURE;
+	}
+	if (io_g_offset > 0 && io_g_offset > 0x3f - sc_io_lat.rt_iocomp) {
+		printk(BIOS_ERR, "%s: IO COMP overflow\n", __func__);
+		printk(BIOS_ERR, "io_g_offset: %d\n", io_g_offset);
+		printk(BIOS_ERR, "rt_iocomp: %u\n", sc_io_lat.rt_iocomp);
+		return RAMINIT_STATUS_RCVEN_FAILURE;
+	}
+	sc_io_lat.rt_iocomp += io_g_offset;
+	ctrl->rt_io_comp[channel] = sc_io_lat.rt_iocomp;
+	for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+		if (ctrl->rankmap[channel] & BIT(rank))
+			ctrl->io_latency[channel][rank] = io_lat[rank] - io_g_offset;
+
+		const uint8_t shift = rank * 4;
+		sc_io_lat.raw &= ~(0xf << shift);
+		sc_io_lat.raw |= ctrl->io_latency[channel][rank] << shift;
+	}
+	mchbar_write32(SC_IO_LATENCY_ch(channel), sc_io_lat.raw);
+	return RAMINIT_STATUS_SUCCESS;
+}
+
+#define RL_START (256 + 24)
+#define RL_STOP  (384 + 24)
+#define RL_STEP  8
+
+#define RE_NUM_SAMPLES	6
+
+static enum raminit_status verify_high_region(const int32_t center, const int32_t lwidth)
+{
+	if (center > RL_STOP) {
+		/* Check if center of high was found where it should be */
+		printk(BIOS_ERR, "RcvEn: Center of high (%d) higher than expected\n", center);
+		return RAMINIT_STATUS_RCVEN_FAILURE;
+	}
+	if (lwidth <= 32) {
+		/* Check if width is large enough */
+		printk(BIOS_ERR, "RcvEn: Width of high region (%d) too small\n", lwidth);
+		return RAMINIT_STATUS_RCVEN_FAILURE;
+	}
+	if (lwidth >= 96) {
+		/* Since we're calibrating a phase, a too large region is a problem */
+		printk(BIOS_ERR, "RcvEn: Width of high region (%d) too large\n", lwidth);
+		return RAMINIT_STATUS_RCVEN_FAILURE;
+	}
+	return RAMINIT_STATUS_SUCCESS;
+}
+
+static void program_io_latency(struct sysinfo *ctrl, const uint8_t channel, const uint8_t rank)
+{
+	const uint8_t shift = rank * 4;
+	const uint8_t iolat = ctrl->io_latency[channel][rank];
+	mchbar_clrsetbits32(SC_IO_LATENCY_ch(channel), 0xf << shift, iolat << shift);
+}
+
+static void program_rl_delays(struct sysinfo *ctrl, const uint8_t rank, const uint16_t rl_delay)
+{
+	for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+		if (!rank_in_ch(ctrl, rank, channel))
+			continue;
+
+		for (uint8_t byte = 0; byte < ctrl->lanes; byte++)
+			update_rxt(ctrl, channel, rank, byte, RXT_RCVEN, rl_delay);
+	}
+}
+
+static bool sample_dqs(const uint8_t channel, const uint8_t byte)
+{
+	return (get_data_train_feedback(channel, byte) & 0x1ff) >= BIT(RE_NUM_SAMPLES - 1);
+}
+
+enum raminit_status train_receive_enable(struct sysinfo *ctrl)
+{
+	const struct reut_box reut_addr = {
+		.col = {
+			.start    = 0,
+			.stop     = 1023,
+			.inc_rate = 0,
+			.inc_val  = 1,
+		},
+	};
+	const struct wdb_pat wdb_pattern = {
+		.start_ptr  = 0,
+		.stop_ptr   = 9,
+		.inc_rate   = 32,
+		.dq_pattern = BASIC_VA,
+	};
+
+	const uint16_t bytemask = BIT(ctrl->lanes) - 1;
+	const uint8_t fine_step = 1;
+
+	const uint8_t rt_delta = is_hsw_ult() ? 4 : 2;
+	const uint8_t rt_io_comp = 21 + rt_delta;
+	const uint8_t rt_latency = 16 + rt_delta;
+	setup_io_test(
+		ctrl,
+		ctrl->chanmap,
+		PAT_RD,
+		2,
+		RE_NUM_SAMPLES + 1,
+		&reut_addr,
+		0,
+		&wdb_pattern,
+		0,
+		8);
+
+	for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+		if (!does_ch_exist(ctrl, channel))
+			continue;
+
+		for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+			union ddr_data_control_2_reg data_control_2 = {
+				.raw = ctrl->dq_control_2[channel][byte],
+			};
+			data_control_2.force_rx_on = 1;
+			mchbar_write32(DQ_CONTROL_2(channel, byte), data_control_2.raw);
+		}
+		union ddr_data_control_0_reg data_control_0 = {
+			.raw = ctrl->dq_control_0[channel],
+		};
+		if (ctrl->lpddr) {
+			/**
+			 * W/A for b4618574 - @todo: remove for HSW ULT C0
+			 * Can't have force_odt_on together with leaker, disable LPDDR
+			 * mode during this training step. lpddr_mode is restored
+			 * at the end of this function from the host structure.
+			 */
+			data_control_0.lpddr_mode = 0;
+			mchbar_write32(DDR_DATA_ch_CONTROL_0(channel), data_control_0.raw);
+		}
+		data_control_0.force_odt_on     = 1;
+		data_control_0.rl_training_mode = 1;
+		mchbar_write32(DDR_DATA_ch_CONTROL_0(channel), data_control_0.raw);
+		mchbar_write32(SC_IO_LATENCY_ch(channel), (union sc_io_latency_reg) {
+			.rt_iocomp = rt_io_comp,
+		}.raw);
+	}
+	enum raminit_status status = RAMINIT_STATUS_SUCCESS;
+	for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+		if (!does_rank_exist(ctrl, rank))
+			continue;
+
+		/*
+		 * Set initial roundtrip latency values. Assume -4 QCLK for worst board
+		 * layout. This is calculated as HW_ROUNDT_LAT_DEFAULT_VALUE plus:
+		 *
+		 *   DDR3: Default + (2 * tAA) + 4 QCLK + PI_CLK + N-mode value * 2
+		 * LPDDR3: Default + (2 * tAA) + 4 QCLK + PI_CLK + tDQSCK_max
+		 *
+		 * N-mode is 3 during training mode. Both channels use the same timings.
+		 */
+		/** TODO: differs for LPDDR **/
+		const uint32_t tmp = MAX(ctrl->multiplier, 4) + 5 + 2 * ctrl->tAA;
+		const uint32_t initial_rt_latency = MIN(rt_latency + tmp, 0x3f);
+
+		uint8_t chanmask = 0;
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			chanmask |= select_reut_ranks(ctrl, channel, BIT(rank));
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			ctrl->io_latency[channel][rank] = 0;
+			mchbar_write8(SC_ROUNDT_LAT_ch(channel) + rank, initial_rt_latency);
+			ctrl->rt_latency[channel][rank] = initial_rt_latency;
+		}
+
+		printk(BIOS_DEBUG, "Rank %u\n", rank);
+		printk(BIOS_DEBUG, "Steps 1 and 2: Find middle of high region\n");
+		printk(RCVEN_PLOT, "Byte");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(RCVEN_PLOT, "\t");
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++)
+				printk(RCVEN_PLOT, "%u ", byte);
+		}
+		printk(RCVEN_PLOT, "\nRcvEn\n");
+		struct phase_train_data region_data[NUM_CHANNELS][NUM_LANES] = { 0 };
+		for (uint16_t rl_delay = RL_START; rl_delay < RL_STOP; rl_delay += RL_STEP) {
+			printk(RCVEN_PLOT, " % 3d", rl_delay);
+			program_rl_delays(ctrl, rank, rl_delay);
+			run_io_test(ctrl, chanmask, BASIC_VA, true);
+			for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+				if (!rank_in_ch(ctrl, rank, channel))
+					continue;
+
+				printk(RCVEN_PLOT, "\t");
+				for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+					const bool high = sample_dqs(channel, byte);
+					printk(RCVEN_PLOT, high ? ". " : "# ");
+					phase_record_pass(
+						&region_data[channel][byte],
+						high,
+						rl_delay,
+						RL_START,
+						RL_STEP);
+				}
+			}
+			printk(RCVEN_PLOT, "\n");
+		}
+		printk(RCVEN_PLOT, "\n");
+		printk(BIOS_DEBUG, "Update RcvEn timing to be in the center of high region\n");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(BIOS_DEBUG, "C%u.R%u: \tLeft\tRight\tWidth\tCenter\n",
+				channel, rank);
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+				struct phase_train_data *const curr_data =
+						&region_data[channel][byte];
+				phase_append_current_to_initial(curr_data, RL_START, RL_STEP);
+				const int32_t lwidth = range_width(curr_data->largest);
+				const int32_t center = range_center(curr_data->largest);
+				printk(BIOS_DEBUG, "   B%u: \t%d\t%d\t%d\t%d\n",
+					byte,
+					curr_data->largest.start,
+					curr_data->largest.end,
+					lwidth,
+					center);
+
+				status = verify_high_region(center, lwidth);
+				if (status) {
+					printk(BIOS_ERR,
+						"RcvEn problems on channel %u, byte %u\n",
+						channel, byte);
+					goto clean_up;
+				}
+				ctrl->rcven[channel][rank][byte] = center;
+				update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+			}
+			printk(BIOS_DEBUG, "\n");
+		}
+
+		printk(BIOS_DEBUG, "Step 3: Quarter preamble - Walk backwards\n");
+		printk(RCVEN_PLOT, "Byte");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(RCVEN_PLOT, "\t");
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++)
+				printk(RCVEN_PLOT, "%u ", byte);
+		}
+		printk(RCVEN_PLOT, "\nIOLAT\n");
+		bool done = false;
+		while (!done) {
+			run_io_test(ctrl, chanmask, BASIC_VA, true);
+			done = true;
+			for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+				if (!rank_in_ch(ctrl, rank, channel))
+					continue;
+
+				printk(RCVEN_PLOT, "  %2u\t", ctrl->io_latency[channel][rank]);
+				uint16_t highs = 0;
+				for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+					const bool high = sample_dqs(channel, byte);
+					printk(RCVEN_PLOT, high ? "H " : "L ");
+					if (high)
+						highs |= BIT(byte);
+				}
+				if (!highs)
+					continue;
+
+				done = false;
+
+				/* If all bytes sample high, adjust timing globally */
+				if (highs == bytemask && ctrl->io_latency[channel][rank] < 14) {
+					ctrl->io_latency[channel][rank] += 2;
+					ctrl->io_latency[channel][rank] %= 16;
+					program_io_latency(ctrl, channel, rank);
+					continue;
+				}
+
+				/* Otherwise, adjust individual bytes */
+				for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+					if (!(highs & BIT(byte)))
+						continue;
+
+					if (ctrl->rcven[channel][rank][byte] < 128) {
+						printk(BIOS_ERR,
+							"RcvEn underflow: walking backwards\n");
+						printk(BIOS_ERR,
+							"For channel %u, rank %u, byte %u\n",
+							channel, rank, byte);
+						status = RAMINIT_STATUS_RCVEN_FAILURE;
+						goto clean_up;
+					}
+					ctrl->rcven[channel][rank][byte] -= 128;
+					update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+				}
+			}
+			printk(RCVEN_PLOT, "\n");
+		}
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(BIOS_DEBUG, "\nC%u:  Preamble\n", channel);
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+				printk(BIOS_DEBUG,
+					" B%u: %u\n", byte, ctrl->rcven[channel][rank][byte]);
+			}
+		}
+		printk(BIOS_DEBUG, "\n");
+
+		printk(BIOS_DEBUG, "Step 4: Add 1 qclk\n");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+				ctrl->rcven[channel][rank][byte] += 64;
+				update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+			}
+		}
+		printk(BIOS_DEBUG, "\n");
+
+		printk(BIOS_DEBUG, "Step 5: Walk forward to find rising edge\n");
+		printk(RCVEN_PLOT, "Byte");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(RCVEN_PLOT, "\t");
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++)
+				printk(RCVEN_PLOT, "%u ", byte);
+		}
+		printk(RCVEN_PLOT, "\n inc\n");
+		uint16_t ch_result[NUM_CHANNELS] = { 0 };
+		uint8_t inc_preamble[NUM_CHANNELS][NUM_LANES] = { 0 };
+		for (uint8_t inc = 0; inc < 64; inc += fine_step) {
+			printk(RCVEN_PLOT, " %2u\t", inc);
+			run_io_test(ctrl, chanmask, BASIC_VA, true);
+			done = true;
+			for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+				if (!rank_in_ch(ctrl, rank, channel))
+					continue;
+
+				for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+					if (ch_result[channel] & BIT(byte)) {
+						/* Skip bytes that are already done */
+						printk(RCVEN_PLOT, ". ");
+						continue;
+					}
+					const bool pass = sample_dqs(channel, byte);
+					printk(RCVEN_PLOT, pass ? ". " : "# ");
+					if (pass) {
+						ch_result[channel] |= BIT(byte);
+						continue;
+					}
+					ctrl->rcven[channel][rank][byte] += fine_step;
+					update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+					inc_preamble[channel][byte] = inc;
+				}
+				printk(RCVEN_PLOT, "\t");
+				if (ch_result[channel] != bytemask)
+					done = false;
+			}
+			printk(RCVEN_PLOT, "\n");
+			if (done)
+				break;
+		}
+		printk(BIOS_DEBUG, "\n");
+		if (!done) {
+			printk(BIOS_ERR, "Error: Preamble edge not found for all bytes\n");
+			printk(BIOS_ERR, "The final RcvEn results are as follows:\n");
+			for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+				if (!rank_in_ch(ctrl, rank, channel))
+					continue;
+
+				printk(BIOS_ERR, "Channel %u Rank %u:  preamble\n",
+					channel, rank);
+				for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+					printk(BIOS_ERR, " Byte %u: %u%s\n", byte,
+						ctrl->rcven[channel][rank][byte],
+						(ch_result[channel] ^ bytemask) & BIT(byte)
+							? ""
+							: " *** Check this byte! ***");
+				}
+			}
+			status = RAMINIT_STATUS_RCVEN_FAILURE;
+			goto clean_up;
+		}
+
+		printk(BIOS_DEBUG, "Step 6: center on preamble and clean up rank\n");
+		for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			printk(BIOS_DEBUG, "C%u:  Preamble increment\n", channel);
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+				/*
+				 * For Traditional, pull in RcvEn by 64. For ULT, take the DQS
+				 * drift into account to the specified guardband: tDQSCK_DRIFT.
+				 */
+				ctrl->rcven[channel][rank][byte] -= tDQSCK_DRIFT;
+				update_rxt(ctrl, channel, rank, byte, RXT_RESTORE, 0);
+				printk(BIOS_DEBUG, " B%u: %u      %u\n", byte,
+					ctrl->rcven[channel][rank][byte],
+					inc_preamble[channel][byte]);
+			}
+			printk(BIOS_DEBUG, "\n");
+		}
+		printk(BIOS_DEBUG, "\n");
+	}
+
+clean_up:
+	for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+		if (!does_ch_exist(ctrl, channel))
+			continue;
+
+		if (ctrl->lpddr) {
+			/**
+			 * W/A for b4618574 - @todo: remove for HSW ULT C0
+			 * Can't have force_odt_on together with leaker, disable LPDDR mode for
+			 * this training step. This write will disable force_odt_on while still
+			 * keeping LPDDR mode disabled. Second write will restore LPDDR mode.
+			 */
+			union ddr_data_control_0_reg data_control_0 = {
+				.raw = ctrl->dq_control_0[channel],
+			};
+			data_control_0.lpddr_mode = 0;
+			mchbar_write32(DDR_DATA_ch_CONTROL_0(channel), data_control_0.raw);
+		}
+		mchbar_write32(DDR_DATA_ch_CONTROL_0(channel), ctrl->dq_control_0[channel]);
+		for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+			mchbar_write32(DQ_CONTROL_2(channel, byte),
+					ctrl->dq_control_2[channel][byte]);
+		}
+	}
+	io_reset();
+	if (status)
+		return status;
+
+	printk(BIOS_DEBUG, "Step 7: Sync IO latency across all ranks\n");
+	for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+		if (!does_ch_exist(ctrl, channel))
+			continue;
+
+		status = change_rcven_timing(ctrl, channel);
+		if (status)
+			return status;
+	}
+	printk(BIOS_DEBUG, "\nFinal Receive Enable and IO latency settings:\n");
+	for (uint8_t channel = 0; channel < NUM_CHANNELS; channel++) {
+		if (!does_ch_exist(ctrl, channel))
+			continue;
+
+		for (uint8_t rank = 0; rank < NUM_SLOTRANKS; rank++) {
+			if (!rank_in_ch(ctrl, rank, channel))
+				continue;
+
+			const union sc_io_latency_reg sc_io_latency = {
+				.raw = mchbar_read32(SC_IO_LATENCY_ch(channel)),
+			};
+			printk(BIOS_DEBUG, "  C%u.R%u: IOLAT = %u  rt_iocomp = %u\n", channel,
+				rank, ctrl->io_latency[channel][rank], sc_io_latency.rt_iocomp);
+			for (uint8_t byte = 0; byte < ctrl->lanes; byte++) {
+				printk(BIOS_DEBUG, "   B%u:   %u\n", byte,
+					ctrl->rcven[channel][rank][byte]);
+			}
+			printk(BIOS_DEBUG, "\n");
+		}
+	}
+	return status;
+}
diff --git a/src/northbridge/intel/haswell/registers/mchbar.h b/src/northbridge/intel/haswell/registers/mchbar.h
index a81559bb1e..9172d4f2b0 100644
--- a/src/northbridge/intel/haswell/registers/mchbar.h
+++ b/src/northbridge/intel/haswell/registers/mchbar.h
@@ -18,6 +18,8 @@
 #define RX_TRAIN_ch_r_b(ch, rank, byte)		_DDRIO_C_R_B(0x0000, ch, rank, byte)
 #define TX_TRAIN_ch_r_b(ch, rank, byte)		_DDRIO_C_R_B(0x0020, ch, rank, byte)
 
+#define DDR_DATA_TRAIN_FEEDBACK(ch, byte)	_DDRIO_C_R_B(0x0054, ch, 0, byte)
+
 #define DQ_CONTROL_2(ch, byte)			_DDRIO_C_R_B(0x0064, ch, 0, byte)
 #define DQ_CONTROL_0(ch, byte)			_DDRIO_C_R_B(0x0074, ch, 0, byte)
 
@@ -100,6 +102,7 @@
 #define COMMAND_RATE_LIMIT_ch(ch)		_MCMAIN_C(0x4010, ch)
 #define TC_BANK_RANK_D_ch(ch)			_MCMAIN_C(0x4014, ch)
 #define SC_ROUNDT_LAT_ch(ch)			_MCMAIN_C(0x4024, ch)
+#define SC_IO_LATENCY_ch(ch)			_MCMAIN_C(0x4028, ch)
 
 #define REUT_ch_PAT_WDB_CL_MUX_CFG(ch)		_MCMAIN_C(0x4040, ch)
 
-- 
2.39.2

